1. Field of the Invention
The present invention relates to a voice over Internet protocol (hereinafter, referred to VoIP) service, and more particularly to a head end apparatus for a media gateway control protocol (hereinafter, referred to MGCP) type call service.
2. Description of the Related Art
As very high speed Internet service has become widely provided, use of VoIP service has rapidly spread through the Internet. For a protocol to provide the VoIP service, H.323, MGCP, and SIP (session initiation protocol) are used. In a cable network, the MGCP type is selected as a packet-cable specification and is scheduled for service.
Presently-used Internet service modes for subscribers are mainly divided into an ADSL (asymmetric digital subscriber line) mode, a cable MODEM mode and a private LAN (local area Network) mode. The ADSL mode is widely used in homes in Korea, the cable MODEM mode is widely used in homes in the Americas and Europe, and the private LAN mode is widely used in companies. Although a PPP (point-to-point protocol) mode using PSTN (public switched telephone network)/ISDN (integrated services digital network) was widely used in the past, the use of the PPP mode has gradually been reduced.
An ISP (Internet service provider) providing the Internet service through the ADSL and the cable MODEM uses a DHCP (dynamic host configuration protocol) mode in order to provide very high speed data communication service to many subscribers while using a limited number of authorized IP (Internet Protocol) addresses. According to the DHCP mode, the authorized IP address is assigned to the subscriber only when the subscriber uses a computer in order to efficiently distribute the limited authorized IP addresses. When the ISP installs a backbone router using a NAT (network address translator) function, data transmission speed will be lowered and network games are not executable due to packet loss and delay, so the ISP assigns the authorized IP address to the subscriber by using the DHCP without using the NAT function.
Recently, many Internet users want to have the data communication service together with the VoIP service. The VoIP is a main technique for Internet telephony, because it supports the providing of data together with voice through the Internet by using the IP.
If the ISP operates the VoIP network using the DHCP mode for providing the data communication service, in which the authorized IP address is assigned to the subscriber without using the NAT function, the IP address is continuously assigned to the VoIP terminal as long as the VoIP terminal is connected to the network, so that the ISP lacks the authorized IP addresses.